An interactive wireless communication network system includes a host unit for collecting information and a plurality of wireless nodes, and the wireless nodes in particular comprise a master unit for performing overall network processing among a group of wireless nodes, and a plurality of slave units dependent thereupon. With such a wireless node configuration, the master unit establishes an ad-hoc network with each slave unit as necessary to perform interactive wireless communication with each slave unit, and performs interactive communication with the host unit representing the wireless node group. Thus, the master unit collects information from the slave units, and performs transmission to the host unit representing the slave units, thereby reducing the load on the slave units, and enabling the slave units to be configured at low cost and in a simplified manner. However, with this method, because processes are concentrated in a single master unit, and the traffic volume of transmission/reception in the master unit is exceedingly large compared to the slave units, if there is shortage in the remaining power of a battery serving as a power source for the master unit, problems occur such as slowdown of the entire network due to master unit transmission/reception output shortage, or at worst, disconnection of the communication circuit due to master unit battery rundown. Therefore, power management of the wireless nodes has been essential.
Thus, there has been a conventional power management method for wireless nodes such as the invention of patent document 1. FIG. 24 is a constitutional diagram of a conventional power management method for wireless nodes described in patent document 1. The system shown in FIG. 24 is an interactive wireless communication network comprising a plurality of wireless nodes 2401, host unit 2402, and gateway unit 2403 serving as relay between the host unit and wireless nodes, wherein the wireless node that initially sends a transmission request serves as a provisional master unit 2404 that is a provisional master wireless node, and other wireless nodes serve as slave units 2405, and interactive communications between the provisional master unit 2404 and each slave unit 2405 commence. Thereafter, the provisional master unit 2404 collects battery power data of all the slave units, reselects in accordance with the collected data a slave unit with the best operating conditions to be an actual master unit 2406 to serve as an actual master wireless node, and switches to interactive wireless communication between the actual master unit 2406 serving as a hub and each slave unit so that the actual master unit 2406 performs interactive wireless communication with the host unit 2402 via the gateway unit 2403. Thereafter, an actual master unit is periodically reselected in the same manner, thereby allowing selection of an appropriate wireless node as a master unit that is less susceptible to battery rundown.
Patent Document 1: Laid-open Japanese Patent No. H10-145276
However, with such a conventional constitution as described above, the more slave units there are, the less opportunity each slave unit has to be selected as an actual master unit. This leads to the problem that the effect of eliminating imbalances in power consumption by having slave units with excess battery power switch to serve as an actual master unit is not fully and efficiently demonstrated.
Further, because in such a constitution an actual master unit is selected from among all the slave units, in a case where wireless nodes are distributed across a wide range, the average wireless communication distance between the actual master unit and slave units becomes longer and the power consumption for the entire network required for wireless transmission increases, so that on average any wireless node is likely to experience battery rundown at an early stage.
Further, in a case where a slave unit is outside the radio wave range given the transmission power of the selected actual master unit, such slave unit needs to be separated from the network even when it has sufficient battery power, or the actual master unit and slave units need to be physically moved each time to a location where reception can be obtained, resulting in the problem of considerably degraded network performance and convenience.
The present invention was conceived with a view toward solving such conventional problems, and its object is to provide an interactive wireless communication network comprising a plurality of wireless nodes, wherein imbalance in power consumption of the wireless nodes is efficiently prevented, power consumption of the entire network is reduced to prolong average battery life, thus enabling interactive wireless communication to be always available between master unit and slave units.